It is known that polymers having conjugated double bonds such as polyacetylene, polypyrrole, polythiophene and polyaniline become electrically conductive when doped with ions. It has been a common practice to utilize such electrically conductive polymers as an electrode active substance for a secondary battery, a solid electrolyte for an electrolytic capacitor, an antistatic agent, etc.
Among these electrically conductive polymers, polypyrrole exhibits a relatively high stability of electric conductivity in the air and thus has been practically used as a solid electrolyte for an electrolytic aluminum capacitor or an active positive electrode substance for a secondary battery.
However, an electrically conductive polymer is disadvantageous in that it is normally infusible and insoluble in a solvent and thus has a limited moldability. Consequently, it is difficult to obtain a product having a desired shape. Thus, in the present state of the art a polymer is deposited on the surface of an electrode by electrolytic polymerization. The polymer is then peeled off the electrode to obtain a film which is used as is. Alternatively, a powdered polymer obtained by chemical oxidation-polymerization is used.
Furthermore, JP-A-63-101415 (corresponding to U.S. Pat. Nos. 4,697,001 and 4,710,401; the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a process for preparing an electrically conductive polymer from 3-alkyl or 3,4-dialkyl-substituted pyrrole, which comprises oxidation-polymerizing 3-alkyl or 3,4-dialkyl-substituted pyrrole in a solvent to obtain a precipitate, separating the precipitate, and then drying the precipitate to prepare an electrically conductive polymer or which comprises contacting liquid 3-alkyl or 3,4-dialkyl-substituted pyrrole with a porous substrate, and then oxidation-polymerizing the liquid 3-alkyl or 3,4-dialkyl-substituted pyrrole impregnated into the substrate to polypyrrole, to thereby prepare a composite of an electrically conductive polypyrrole.
The present inventors found that by the chemical oxidation polymerization of 3-alkyl or 3,4-dialkyl-substituted pyrrole (hereinafter referred to as "alkyl-substituted pyrrole") in an organic solvent such as alcohol in the presence of a oxidation-polymerization agent an ion-doped polymer is obtained which exhibits little or no solubility in most ordinary organic solvents. Therefore, an ion-doped polypyrrole obtained by a process which comprises subjecting an alkyl-substituted pyrrole to polymerization reaction in a solvent to obtain a precipitate which precipitate is then separated from the reaction system, cannot be dissolved in most ordinary organic solvents. Consequently, this material cannot be molded using a solvent. In order to obtain a molded product of an ion-doped polypyrrole, a method can be employed which comprises compression-molding a powdered ion-doped polypyrrole produced by a polymerization reaction. However, the ion-doped polypyrrole cannot be molded using solvent and thus has limited moldability.